Tue, February 18, 2014 Turnagain Pass Avalanche Forecast

Tue, February 18th, 2014

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


Travel Advice	Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.	Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.	Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.	Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.	Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches	Natural and human-triggered avalanches unlikely.	Natural avalanches unlikely; human-triggered avalanches possible.	Natural avalanches possible; human-triggered avalanches likely.	Natural avalanches likely; human-triggered avalanches very likely.	Natural and human-triggered avalanches certain.
Avalanche Size and Distribution	Small avalanches in isolated areas or extreme terrain.	Small avalanches in specific areas; or large avalanches in isolated areas.	Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.	Large avalanches in many areas; or very large avalanches in specific areas.	Very large avalanches in many areas.

Avalanche Problem 1

Storm Slabs

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

More info at Avalanche.org

Another round of snow is expected to come in fast and furious today. Winds, combined with high snowfall rates will rapidly load slopes and quickly increase avalanche danger. If the forecast verifies, instability will be on the rise for all the classic storm snow avalanche concerns:

Wind slabs:
Winds out of the East are currently increasing. With ample snow available for transport, naturally occurring wind slab avalanches 1-3′ thick are possible on leeward slopes and rollovers, also watch for cross-loading in gullies. I’d expect much of today’s avalanche activity to be in the form of wind slabs of varying thickness.

Storm Slabs:
Snowfall today will be falling on low density powder from Sunday night. Though today’s snow is expected to be low density as well and not prime conditions for creating storm slabs, the simple “rapid loading” that is expected has the potential to do this – even without the presence of wind. These slabs will be soft and could occur naturally on steep slopes at all elevations.

Loose Snow avalanches:
Loose snow sluffs should be expected. The biggest concern with these is the possibility for initiating either a storm slab or a persistent slab on the descent.

Cornices:
Today will be ideal cornice growth and calving conditions. The main concern with cornices also has to do with the possibility for triggering a larger slab below.

*Note: The AKDOT webcam is working again on Turnagain Pass! Keep tabs on snowfall as well as the road conditions with this link.

Avalanche Problem 2

Persistent Slabs

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

More info at Avalanche.org

Today we will be adding yet another load to our tenuous snowpack and potentially overloading the weak snow that sits just above the thick January crust. This weak layer of faceted snow has been well documented over the past two weeks and sits below all the February storm snow – between 2 and 3 feet deep. These persistent slab avalanches have the ability to propagate over entire slopes and be around 2-3′ deep (deeper with any additional snow).

In the event the storm today does not produce, this avalanche problem will be the primary concern. We have already seen multiple large remotely triggered slides occur in this mid-pack weak layer and today will be no different.

Weather

Tue, February 18th, 2014

Updated storm totals beginning Sunday evening through yesterday mid-day:

Turnagain Pass – 14″ (Eddie’s), 12″ (Tincan) and 10″ on (Sunburst)

Girdwood Valley mid to upper elevations – 8-9″

Summit Lake – 3-5″

During the past 24-hours we have seen a short break between storms. Temperatures have hovered in the mid-teens on the ridgetops and mid-20’s at 1,000′. Ridgetop winds have averaged 10mph with a max gust of 32mph from the East and Southeast. Overnight, clouds have filled back in with the beginning of the next system, which is on our doorstep.

Today and into tonight another round of heavy snow (1+” of water weight) is on tap. As of 6am this morning 4″ has fallen on Turnagain Pass with only ~2″ in Girdwood and a trace at Summit Lake. We should see between 10-18″ by tonight – at least on the Pass. Ridgetop winds are just beginning to increase and are expected to average around 40mph from the East. Temperatures look to remain in the mid to lower teens above treeline and the mid-20’s at 1,000′, which will allow for snowfall to be low density.

Snow showers should taper off tomorrow (Wednesday) and models show a break between storms Thursday before another system moves in Friday with snow possible.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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